The Blade Guard Tissue

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The epidermal cells of most species have no chloroplast . However, in the hydrophytes submerged in hygrophilous cells have chloroplasts. The cuticle is generally thicker on the adaxial epidermis . In humid plants the cuticle is thin, whereas in plants adapted to climates aggregates, the cuticle can be so thick that gives the leaves a leathery consistency. 21 The epidermis is generally formed by a single layer of cells, but can be multiple or multistratified as in the case of Nerium and Ficus . In Peperomia the epidermis can have up to fifteen multiple cell layers, while still thicker than the cloud .

The stomata are groups of two or more specialized epidermal cells morphological and physiological and whose function is to regulate gas exchange and transpiration of the plant. Are found in all the green parts of the plant carriers, particularly on the leaves, which can be in one or both sides, most commonly in the underside . The number of stomata can vary between 22 and 2230 per mm 2 of leaf surface, depending both on the species considered in environmental conditions. The parasitic plants without chlorophyll as Monotropa ...
... and Neottia have no stomata, while ( Orobanche has them only in the stem. In the remaining autotrophic plants, the aerial parts without chlorophyll, such as variegated leaves, may have stomata but these are not functional, like those found in the petals . 22
Paralelinervadas leaves monocots, dicots and some conifers with needle-like leaves have stomata arranged in parallel rows, whereas in dicots with reticulate venation leaf stomata are scattered. In plants growing in climates with an average humidity ( mesophytic ) the stomata are arranged at the same level as other epidermal cells, but in many gymnosperms and leaves of plants xerophytes , the stomata are sunken and as suspended of attached cells that form a dome or, are hidden in crypts. In plants of wet environments, finally, the stomata are raised regarding the level of other epidermal cells. 23
Stomata consist of two specialized cells called guard cells that delimit an opening called ostiole or pore . Adjacent to the guard cells, and functionally related to them, many species have two or more cells called cells attached , subsidiaries or attached . Below there is ample room ostiole called intercellular substomatal chamber , which communicates the system of intercellular spaces of the mesophyll with the outside air. When the stomata are arranged in rows, stomatal chambers are interconnected. 23
In surface view the guard cells of dicots, gymnosperms, monocots and pteridophytes many kidney-shaped, sausage or banana with rounded ends. They usually have external cuticular surface a flange sometimes forms a true dome or stomatal lobby . The cuticle extends over the ostiole and sometimes form protrusions on the inside, forming an interior hallway . Even cells that limit lining inside the chamber substomatal. 24 The guard cells of grasses are elongated, with bulbous ends are connected by pores, resulting from an incomplete development of the cell wall , so that both cells constitute a physiological unit. The cell walls are thin to thick bulbous ends in the middle region. 22 The sedges , like grass, guard cells and nuclei are shaped weights, but the arrangement of the microfibrils of cellulose is different. 25
The cell wall of the guard cells which delimits the ostiole is, in all cases, thicker than the opposite wall of which is thinner and more flexible than the tangential walls. This feature is related to the ability of the guard cells to change shape and increase its volume to control the size of ostiole. Stomatal movements result from changes in the turgor relative to the guard cells and appended caused by changes in the osmotic potential. 26 has been shown that plasmodesmata that connect with their neighboring guard cells are disrupted to maturity stoma, the absence of intercellular communication with other cells is what allows the occlusive function independently to control their turgor. 27
The stomata are classified according to the number and arrangement of cells attached. It is said anomocítico or ranunculáceo when no cells attached, is the most common in dicots and some monocots such as Amaryllidaceae and dioscoreáceas . When the stoma has two adjoining cells arranged parallel with respect to the stops, is called paracítico or rubiáceo . If you have attached three cells, one of which is called smaller anisocítico and is characteristic of crucifers and Solanaceae . The stoma tetracytic has four subsidiary cells and is common in several families of monocotyledons as Araceae , commelináceas and Musa . The cell has two adjoining diacítico perpendicular to the stops and is in the families of Caryophyllaceae and Acanthaceae . The last two types of stomatal subsidiary cells exhibit mumerosas. The type ciclocítico , arranged in one or two circles around the guard cells, whereas helicocítico arranges in a spiral around the stops.

Trichomes or hairs are appendages of the skin that can take various forms, structures and functions. They originate from epidermal meristemoides, starting out as a lump that enlarges and may or may not be divided. The cells that make the hairs can remain alive at maturity or losing the contents of their cytoplasm. There are several types of trichomes and the same plant can have several of them. Also, the types of trichomes vary between different species , so are useful in taxonomy , to characterize and identify species and genera . The leaf hairs are said no glabra .

With regard to its structure, trichomes cellulose cell walls, which are coated with a cuticle or lignified secondary walls. Sometimes the walls are impregnated with silica or calcium carbonate , which gives greater rigidity. The contents of the cytoplasm varies with the function of each type of trichome generally are highly vacuolated, may be crystals or cystoliths. Frequently large celled hairs have cores polyploid .

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